More than 7,000 colleges, universities, technical schools and community colleges from around the world declared a climate emergency in a joint letter which was set to be delivered to the United Nations on Wednesday.

"Declaring a climate emergency changes the nature of the urgency in higher education," Sam Barratt, chief of education and youth for U.N. Environment told the Thomson Reuters Foundation.

Networks of schools pledged to increase sustainability curriculum and campus outreach, boost climate change research and skill-building opportunities for students and reach carbon neutrality by 2050, some as soon as 2030.

"This isn't a nice to-do, it's a must do," Barratt said.

The letter was coordinated by the UN Environment's Youth and Education Alliance, The Alliance for Sustainability and Leadership in Education and Second Nature, a nonprofit working with colleges and universities on climate action.

It was delivered to U.N. ministers at the Higher Education Sustainability Initiative ahead of the United Nations Climate Action Summit on Sept. 23.